The primary objective of the proposed research is to improve understanding of the electronic, thermodynamic and kinetics of the aspects of the mechanism of cooperativeity of hemoglobin. The nature of the bonding between iron and its immediate ligands and the effect of out-of-plane motion of the iron on heme spectra will be investigated by ab initio and semiempirical molecular orbital theory respectively. The latter technique will be used to study the spectra of bile pigments in an effort to help elucidate the structure of the chromophore of phytochrome. The structural significance of the phenomenological parameters of the allosteric model will be investigated and recent experimental information will be analyzed in order to determine at what stage of oxygenation the various salt-bridges of hemoglobin are primarily severed. The applicability of the allosteric model to aspartate transcarbamolyase will be tested by attempting to quantitatively correlate much of the existing data. Finally, the kinetics of the reactions of myoglobin and hemoglobin with various ligands will be analyzed in the framework of transition-state theory in an effort to understand the kinetics in terms of the structure of the protein.